Voltage-electrolyte engineered graphene electrodes for simultaneous detection of nM-level Ponceau 4R and Rhodamine B

Misuse of food colorants threatens public health. Ponceau 4R (PR), a legal red dye, may cause allergies, neurotoxicity, and carcinogenicity in excess. Worse, it is often fraudulently replaced by Rhodamine B (RB), a low-cost industrial dye with stronger carcinogenic and cardiotoxic effects-recent chili product incidents highlight this hazard. Both dyes also enter the ecological environment via washing and food debris, amplifying harm. Thus, simultaneous detection of PR and RB is critical to tackle dual risks from overuse and illicit substitution. Electrochemical sensing is promising, while current modified electrodes only detect PR or RB individually, lacking sensitive co-detection.

Herein, we develop a synergistic voltage-electrolyte strategy to tailor the structural and catalytic properties of electrochemically exfoliated graphene (EEG) for dual-analyte sensing. By modulating exfoliation voltages (3-5 V) and electrolytes (H₂SO₄, NaHSO₄, Na₂SO₄), we precisely controlled graphene thickness, defect density, and exfoliation kinetics. Optimized EEG-2@4V (NaHSO₄, 4 V) features ultrathin layers, abundant defects, a high electroactive surface area, and reduced charge-transfer resistance compared H₂SO₄-derived graphene. This engineered material enables simultaneous detection of PR and RB at unprecedented limits of detection of 3.46 nM and 6.98 nM, respectively. The sensor exhibits minimal signal interference (<5 %) from common food additives and high reproducibility (RSD <3 %). Validated in real chili products, beverage, and wastewater samples, the method achieved recoveries of 95.3-101.2 %, demonstrating its practicality for rapid on-site screening of PR and RB.

This study addresses a critical need for the sensitive, simultaneous detection of PR and RB. The developed sensor platform demonstrates high reliability, efficiency, and validated performance in real samples. This innovation addresses a significant gap in rapid on-site screening for both dyes. Consequently, it facilitates regulatory monitoring to prevent the misuse of food colorants and provides a practical tool for protecting public health as well as environmental integrity related to PR and RB.